HueFill: Rainbow & Gradient Text for Google Docs™

HueFill is an add-on for Google Docs™ that colours the text you select: a rainbow, a gradient of your own colours, or your colours in turn, letter by letter or word by word.

Rainbow text, free: select text and click Colour the selection. As often as you like.
Gradients and your own colours: pick 2 to 5 colours, or start from Sunset, Ocean, Candy, Forest or Fire, and the letters run smoothly from the first to the last, or take them in turn.
Effects: colour the highlight behind the letters instead of the letters, or make the letters grow from one size to another.
A preview in the sidebar shows the look before you colour anything.
Remove colours takes the text and highlight colours off the selection, free.

The colours are ordinary Docs text colours: they stay when the document is shared, printed, downloaded as a PDF or opened without HueFill.

Plans

Free: the rainbow on the letters, unlimited, and Remove colours. Your own colours, gradients, highlights and growing letters: 10 colourings in total per Google account.
HueFill Pro: $9 once per Google account, all of it as often as you like. No subscription or renewal. Refunds within 14 days. See the terms.

Open it from Extensions > HueFill in any document.

Add-on will not open or uses the wrong Google account?